The invention relates to a pressure transducer for generating an electric signal which corresponds to a liquid pressure to be measured in a liquid vessel, said transducer comprising a measuring cell, arranged in an exterior tube, which measuring cell can be filled partially with a pressure transmission liquid and for the remainder with a gas, wherein leading away from the measuring cell there is a liquid pressure transmitting chamber at the measurement end of the exterior tube capable of being filled with the pressure transmission liquid which chamber can be directly connected in pressure transmitting relation with the liquid in the liquid vessel; in the measuring cell, means are arranged for generating an electric signal which corresponds to the gas volume in the measuring cell, the measuring cell comprising an interior tube, surrounded by the exterior tube, whereby, between the exterior and interior tube, a channel is left open for the passage of the pressure transmission liquid during filling of the chamber, the interior tube being closed at its end remote from the measuring end of the pressure transducer.
A pressure transducer of this type, which is a miniature pressure transducer, is known from the German OS No. 2,811,859 which corresponds to the above identified copending application. This pressure transducer exhibits a measuring end with an axial opening which is disposed longitudinally opposite the opening of the measuring cell. However, the pressure transducer, before it is conveyed into a liquid vessel, must itself be filled with a pressure transmission liquid. In so doing, it is easy for the pressure transducer filled with the pressure transmission liquid to incur impact. In the case of impact of the pressure transducer, however, pressure transmission liquid then drops out of the frontal axial opening at the measurement end on account of the special frontal position of the opening. As a consequence, air which is in the measuring cell is drawn out of the open end of the measuring cell. This leads to erroneous measured values. In addition, in the case of a pressure transducer introduced in a liquid vessel, the opening at the measurement end of the exterior tube can readily become clogged. Further, in the case of the pressure transducer of the aforesaid copending application, additional arrangements and special methods must be employed in order to fill the measuring cell partially with the transmission liquid, so that the position of the meniscus between the transmission liquid and air in the measuring cell can be established. This is very difficult and cumbersome.
An additional pressure transducer, which is also a miniature pressure transducer, is known from the German OS No. 2,447,529 and U.S. Pat. No. 3,942,382. In the case of this pressure transducer, a thin capillary tube projects axially into the measuring cell and connects an interior tube, which serves the purpose of supply of the transmission fluid, with the chamber at the measurement end which is capable of being filled with this liquid, which chamber can be directly connected with the liquid vessel; i.e., a blood vessel, via a suitable connector. When the pressure transducer and connector are being filled with transmission fluid, for example a physiological saline solution, this liquid flows via the interior tube through the capillary and into the chamber which is capable of direct communication via the connector with the liquid vessel on account of an axial opening of the pressure transducer at its measurement end. Due to the position of the opening of the pressure transducer, the latter pressure transducer is subject to the same disadvantages as the pressure transducer of the German OS No. 2,811,859. During filling of the pressure transducer with the transmission fluid, a meniscus between this liquid and the gas volume at the end of the capillary tube between the interior wall of the exterior tube and the exterior wall of the capillary tube is to be formed. This meniscus must have a specified position in the measuring cell in order that satisfactory measuring results can be obtained. If the capillary tube, which is to project axially into the measuring cell disposed in the exterior tube, is somewhat bent, or does not lie precisely axially, this can lead to non-linear readings. Furthermore, the pressure transducer is complicated in its structure due to the capillaries.